Hackage lists a reachable maintainer address for siren-json

## Summary

`siren-json.cabal`'s `maintainer:` field carries an address that reaches the maintainer, so the contact Hackage publishes for the package works.

## Motivation

`siren-json.cabal:14` still reads `alunduil@alunduil.com`, which no longer reaches the maintainer. Hackage renders that field on the package page as the contact for the package, so anyone with a question, a security report, or a takeover request has no working route.

Surfaced while filling the Contributor Covenant 2.1 enforcement contact in #79; the Code of Conduct address was corrected there, but cabal metadata is release-facing rather than Code of Conduct scope, so it was left out of that change.

collection-json.hs carries the same stale address at `collection-json.cabal:15`, so this is a shared gap rather than a siren-only one.

## Scope

- Set `maintainer:` in `siren-json.cabal` to `alunduil@gmail.com`.

## Acceptance criteria

- [ ] `siren-json.cabal`'s `maintainer:` field is an address that reaches the maintainer.

## Additional context

`COPYRIGHT:1` also carries the old address, deliberately left alone — it records the notice as asserted in 2017 rather than a live contact channel.

The corrected address reaches Hackage on the next upload, which is manual (`cabal sdist` then `cabal upload --publish`), so the fix does not take effect until the `1.0.0.0` release.

Open siren-json.cabal at line 14 and compare the maintainer field with the acceptance criterion; note that COPYRIGHT:1 is intentionally out of scope. Make the scoped metadata change, inspect the diff, and run cabal sdist to verify the package can still be prepared. Done means the cabal field contains the reachable address and no unrelated files change.

Escrita pelo modelo de indexação a partir do texto da issue.